Low cost on-line non-invasive sewer flow monitoring

1. Low cost on-line non-invasive sewer flow monitoring Andy Nichols, Kirill Horoshenkov, Simon Tait, Simon Shepherd and Yanmin Zhang a.nichols2@bradford.ac.uk • Collaborators: • Open University • Cardiff University • Stanford University • Yorkshire Water Services • Funding: • Yorkshire Water Services • EPSRC grant EP/G015341/1

2. Andy Nichols | a.nichols2@brad.ac.uk ‘Traditional’ flow monitor (submerged acoustic Doppler) • Operates from within the flow. • Estimates flow depth and velocity • Main disadvantages: • Permanent obstruction to the flow • Accumulation of debris – maintenance requirements • Backscatter approach – power requirements

3. Andy Nichols | a.nichols2@brad.ac.uk Airborne Doppler flow monitor • Operates from above the flow • Estimates flow depth and velocity • Main advantages: • Minimal obstruction to the flow – only when surcharged • Minimal accumulation of debris – minimal maintenance • Main disadvantages: • Backscatter approach – power requirements • Assumption of surface pattern behaviour • The free surface pattern does not simply travel along like a car on a motorway. • Features may appear, fluctuate, oscillate, merge, separate, dissipate. • The vertical motion can cause a Doppler shift comparable to that of the horizontal motion. • Above all, the behaviour is not understood, so precisely what the device measures cannot be defined. BUT: Perhaps the surface fluctuation behaviour can be used….

4. Andy Nichols | a.nichols2@brad.ac.uk Measuring temporal surface fluctuations at a point – forward scatter 1. An ultrasonic beam is fired toward the dynamic surface. 2. The signal is reflected to a receiver. 3. The phase of the received signal fluctuates according to the surface. Wave probe 2 1 3 3

5. Andy Nichols | a.nichols2@brad.ac.uk Tracking surface fluctuations • Multiple receivers allow a fluctuation time series to be recorded from multiple known locations on the free surface. • Time series from nearby points can be quite different (hence the issues with the Doppler approach), • BUT similar enough to estimate the temporal lag (by cross-correlation), and hence the surface velocity. 2 wave series separated by a small distance

6. Andy Nichols | a.nichols2@brad.ac.uk Field prototype development

7. Andy Nichols | a.nichols2@brad.ac.uk But can we do more? - Measuring the spatial evolution of the surface pattern So we can measure advection velocity between pairs of reflection points, and can use a time-of-flight technique to measure flow depth, and hence estimate flow rate. BUT We can also cross correlate between pairs of reflection points to obtain a spatial correlation function This describes the nature of the free surface pattern and relates to the underlying turbulence, which is governed by the flow conditions, allowing a number of empirical relationships to be drawn.

8. Andy Nichols | a.nichols2@brad.ac.uk Conclusions • Forward scatter airborne acoustics allow unambiguous measurement of flow surface behaviour. • Tracking the free surface pattern in this manner allows velocity estimation. • Time-of-flight measurements can provide depth data, in order to estimate flow rate. • Further information regarding the flow conditions is encoded in the free surface pattern.

9. Thank You Low cost on-line non-invasive sewer flow monitoring Andy Nichols, Kirill Horoshenkov, Simon Tait, Simon Shepherd and Yanmin Zhang a.nichols2@bradford.ac.uk